There has long been a need to locate leaks in closed refrigeration systems, originally because the loss of refrigerant reduces the cooling capacity of the system, and increasingly because the refrigerants themselves are potential hazardous or deleterious substances when released to the atmosphere. In particular, the production and use of chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants is scheduled for incremental phaseout, and for recovery and recycling in the interim.
Various methods have been used for detecting and locating leaks in a refrigeration system. Since a slow leak of refrigerant is essentially silent and invisible, such methods have included halide torches, electronic sensors, coating exterior joints with material which reacts with the refrigerant, and injecting various types of dye into the refrigeration equipment to locate sites where the dye exits the system.
One of the most effective methods for detecting leaks in refrigeration systems, and a preferred method to be practiced with the present invention, comprises introducing into the refrigeration system an effective amount of a fluorescent dye compound. The dye compound circulates with the refrigerant and oil throughout the refrigeration circuit, and is carried out with escaping refrigerant and oil at a leak site. When the refrigeration system is exposed to ultraviolet light, even a small deposit of the dye compound is brilliantly fluorescent to allow visual detection of the leak. U.S. Pat. No. 5,149,453 discloses such a method for detecting leaks in a refrigeration system, and its content is incorporated herein by reference.
When practicing the above method of leak detection with a fluorescent dye, care has to be taken that the fluorescent dye additive is not allowed to contact the exterior of the refrigeration system as the dye is being introduced into the system. If dye additive is inadvertently spilled or rubbed on the exterior of the system, it will be difficult to distinguish between fluorescence from a leak site and that resulting from inadvertent external contact. This is a particular concern where the dye additive is used for quality assurance checks of air conditioners on newly assembled automobiles, as the air conditioning system's final assembly is usually completed in the automobile assembly line, after which the system is charged with refrigerant and leak detection additive, then operated to circulate the additive and reveal any leaks when viewed under ultraviolet light. While care is normally taken to prevent the refrigerant, lubricant and dye from escaping, the nature of the assembly and charging process creates a risk of spills or inadvertent contamination on clothing or tools. Since very low concentration of dye is required to produce fluorescence, any dye, dyed refrigerant or oil spilled or rubbed on the exterior of the air conditioning system may cause false leak indications.
It is known as disclosed in U.S. Pat. No. 5,650,563, reissued as U.S. Pat. No. Re. 36,951, to place a leak detection dye into a closed air conditioning or refrigeration system prior to the initial charging of the system. This desirably limits the possibility of inadvertent contact between the dye and the exterior of the air conditioner system or personnel responsible for installing and charging the air conditioning system. As discussed in Re. 36,951, it is known to saturate an absorbent wafer, or other suitable substrate carrier, with a mixture of a dye and a solvent, such as a refrigerant system lubricating oil. This system of placing dye on the substrate carrier is sometimes known as a “wet” system because the dye remains in a liquid state.
It is also known to place a leak detection dye onto a wafer by saturating the wafer with a mixture of dye powder and alcohol. Following evaporation of the alcohol, the dye remains in the form of dye solids dispersed through the wafer. This system of placing dye onto a carrier wafer is sometimes referred to as a “dry” system because of the evaporation of the alcohol from the saturating mixture that contains the dye component.
The dye carrying wafer, or other substrate, will remain in the closed air conditioning or refrigeration system. Therefore, following the initial delivery of leak detection dye from the wafer to the system, the presence of the wafer in the closed system will no longer serve a useful purpose. It is desirable, therefore, that the wafer, or other dye carrier substrate, deliver maximum dye concentration while occupying minimum space.